Armored fiber optic assemblies and methods of forming fiber optic assemblies

ABSTRACT

Cables have armor including a polymer, the armor having an armor profile that resembles conventional metal armored cable. The armor provides additional crush and impact resistance for the optical fibers and/or fiber optic assembly therein. The armored cables recover substantially from deformation caused by crush loads. Additionally, the armored fiber optic assemblies can have any suitable flame and/or smoke rating for meeting the requirements of the intended space.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.12/748,925 filed on Mar. 29, 2010, which claims the benefit of U.S.Application No. 61/168,005 filed on Apr. 9, 2009, the content of whichis relied upon and incorporated herein by reference in its entirety.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. 12/261,645,filed Oct. 30, 2008, the entire contents of which are herebyincorporated by reference. This application is also related to U.S.Prov. App. 61/174,059, filed Apr. 30, 2009.

TECHNICAL FIELD

The present disclosure relates generally to optical fiber assemblies,and in particular relates to armored fiber optic assemblies havingpolymeric armor.

BACKGROUND

Fiber optic cables and assemblies should preserve optical performancewhen deployed in the intended environment while also satisfying anyother requirements for the environment. Indoor cables for riser and/orplenum spaces, for example, may require certain flame-retardant ratingsas well as mechanical requirements. Mechanical characteristics such ascrush performance, permissible bend radii, and temperature performancein part determine how installation and use of the cable in theinstallation space affect optical performance of the cable.

Certain conventional indoor riser applications use a fiber optic cabledisposed within a metallic interlocking armor layer. “BX armor” or “TypeAC” cables utilize such armors. BX armor is wound spirally about thefiber optic cable so that the edges of the adjacent wraps of armormechanically interlock to form an armor layer. Interlocking armors arerobust but expensive to install. In particular, the metallic armor mustbe electrically grounded in order to meet safety standards. FIG. 1 showsseveral prior art examples of interlocking armored cables 10 having ametallic (typically aluminum) armor layer 12. The metallic armor layer12 must be grounded, for example, in order to comply with the NationalElectrical Code (NFPA 120) safety standard. Additionally, the metallicarmor 12 can be plastically deformed (i.e., permanently deformed) undercrush loads, which can pinch the cable and cause permanently elevatedlevels of optical attenuation that remain after the crush load isreleased.

Manufacturers have attempted to design dielectric armor cables toovercome the drawbacks of conventional metallic armor constructions.U.S. Pat. No. 7,064,276 discloses a dielectric armor cable having twosynthetic resin layers where the hard resin layer has a continuousspiral groove cut completely through the hard resin layer along thelength of the armor. The hard adjoining edge portions of the spiralgroove abut to inhibit bending below a certain radius. However, oneskilled in the art would recognize this design does not provide thecraft with all of the desired features. Moreover, it can be difficultfor the craft to recognize the cable of U.S. Pat. No. 7,064,276 as anarmored cable layered because it has a smooth outer surface, whereasconventional metal armored cables as depicted by FIG. 1 are easilyidentified by the craft.

SUMMARY

The disclosure is directed to armored fiber optic assemblies having adielectric armor and methods for manufacturing cables having dielectricarmor. The dielectric armor can have an armor profile resemblingconventional metal armored cable. The dielectric armor provides crushand impact resistance to the optical fibers and/or fiber opticassembl(ies) therein. After being subjected to crush loads, thedielectric armor recovers to substantially recover or to wholly recoverits original shape. The dielectric armor is also advantageous in that itprovides desired mechanical performance without requiring the time andexpense of grounding during installation.

According to one aspect, when the dielectric armor is subjected to acrush load along a crush direction that reduces a crush dimension of theassembly from its original outside diameter to less than 62 percent ofthe outside diameter, the cable assembly recovers when the crush load isreleased so that the crush dimension increases to at least 70 percent ofthe outside diameter, and even as high as at least 74 percent of theoutside diameter.

According to another aspect, when the dielectric armor is subjected to acrush load along a crush direction that reduces a crush dimension of theassembly from its original outside diameter to less than 58 percent ofthe outside diameter, the cable assembly recovers when the crush load isreleased so that the crush dimension increases to at least 70 percent ofthe outside diameter.

According to another aspect of the present embodiments, the armoredfiber optic assemblies can have suitable flame and/or smoke ratings forspaces such as plenum and riser applications.

According to another aspect, a method of crush testing armored fiberoptic assemblies comprises: providing an armored fiber optic assemblycomprising a fiber optic assembly having at least one optical fiber anda dielectric armor surrounding the fiber optic assembly; measuring anoutside diameter of the armored fiber optic assembly; subjecting thearmored fiber optic assembly to a crush load along a crush direction;releasing the crush load; allowing the armored fiber optic assembly torecover; and measuring a height of the armored fiber optic assemblyalong the crush direction.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understandingof the invention. The drawings illustrate the various exampleembodiments of the invention and, together with the description, serveto explain the principals and operations of the invention.

FIG. 1 is a perspective view of three different prior art interlockingarmor cables.

FIG. 2 is a side cut-away view of a first example embodiment of anarmored fiber optic assembly having a dielectric armor.

FIG. 3 is a partial cross-section of the armored fiber optic assembly ofFIG. 2 taken along the line 3-3.

FIG. 4 illustrates a test apparatus for applying crush loads to fiberoptic assemblies.

FIG. 5 is an enlarged perspective view and FIG. 6 is a close-up view ofthe armored fiber optic assembly of FIG. 2 showing a partiallongitudinal cross-section of the dielectric armor superimposed on agrid for reference of the shapes of the layers.

FIG. 7 is an enlarged view of a portion of the dielectric armor furthershowing various dimensions associated therewith.

FIG. 8 is an enlarged perspective view of a portion of a generic armoredprofile showing the geometry used for finite-element modeling of thedielectric armor.

FIG. 9 is a schematic diagram of an explanatory extrusion system formaking dielectric armor.

FIG. 10 is a schematic cross-sectional view of the crosshead of theextrusion system of FIG. 9.

FIG. 11 is a schematic side view illustrating another method of formingdielectric armor.

FIG. 12 is a partial, cross-sectional view of another explanatoryexample of a crosshead wherein the profiling feature is within thecrosshead die.

FIG. 13 is a side view of an example extrusion system wherein theprofiling feature is located external to the crosshead and impresses theprofile into the dielectric armor.

FIG. 14 is a perspective view of an example roller-type deforming memberthat is used to impress the armor profile into the dielectric armor.

FIG. 15 is a front view illustrating the use of two roller-typedeforming members to impress the armor profile into the dielectricarmor.

DETAILED DESCRIPTION

Reference is now made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Whenever possible, identical or similar reference numerals areused throughout the drawings to refer to identical or similar parts.

FIG. 2 is a side cut-away view of an armored fiber optic assembly 20having at least one optical fiber 40 disposed within a dielectric armor50. The dielectric armor 50 is non-conductive and has an outer surface52 that includes an armor profile 54 generally formed in a spiral alonga longitudinal axis. As used herein, “armor profile” means that theouter surface has an undulating surface along its length that lookssimilar to conventional metal armors (i.e., a undulating shape along thelength of the armor). The armor profile could also be formed by a seriesof spaced rings. The dielectric armor 50 is advantageous in that it bothprovides crush resistance and recovers to assume its original shape whensubjected to crush loads. The dielectric armor 50 may also meet flameand/or smoke ratings, and does not require electrical grounding.

The dielectric armor 50 includes one or more layers such as an innerlayer 62 and an outer layer 64, but other constructions are possible.The outer layer 64 can be referred to as a “jacket” layer. Thedielectric armor 50 may alternatively consist of a single layer such asthe inner layer 62.

Preferably, the inner layer 62 is a rigid material and the outer jacketlayer 64 is a non-rigid material. It is also possible to use a non-rigidmaterial for the inner layer 62 and to use a rigid material for theouter layer 64. As used herein, “rigid material” means the material hasa Shore D hardness of about 65 or greater and “non-rigid material” meansthe material has a Shore D hardness of about 64 or less. In general theinner layer 62 will be of a more rigid material than the outer jacketlayer 64, or stated alternatively, the Shore D hardness of the innerlayer 62 will be greater than the Shore D hardness of the outer jacketlayer 64. FIG. 2 depicts a dielectric armor 50 having multiple layerswith the armor profile formed essentially in the rigid inner layer 62and in the non-rigid outer layer 64—the outer layer having anessentially uniform thickness over inner layer 62.

Still referring to FIG. 2, a fiber optic assembly 80 is housed withinand protected by the dielectric armor 50. In the illustrated embodiment,the fiber optic assembly 80 is a fiber optic cable having an extrudedpolymer cable jacket 90 and a plurality of tight-buffered optical fibers94 extending longitudinally through the assembly 20 within the cablejacket 90. Strength elements 98, such as aramid fibers, also extendlongitudinally through the cable jacket 90. In one embodiment, the cablejacket 90 can be omitted. By way of example, the fiber optic assembly 80may be a stranded tube cable, monotube cable, micromodule cable, slottedcore cable, loose fibers, tube assemblies, or the like. Additionally,fiber optic assemblies according to the present embodiments can includeany suitable components such as water-blocking or water-swellingcomponents, flame-retardant components such as tapes, coatings, or othersuitable components. The fiber optic assembly 80 may have any suitablefiber count such as 6, 12 or 24-fiber MIC® cables available from CorningCable Systems of Hickory, N.C.

In the illustrated embodiment, the inner layer 62 has a “continuousannular cross-section”. As used herein, “continuous annularcross-section” means there are no spiral grooves, openings, or slitsthat cut entirely through (i.e., from the inner surface to the outersurface 52) the layer 62. The exemplary outer layer 64 is formed from anon-rigid material that provides impact protection, recoverability aftercrush loading, and can also have low-smoke characteristic and/orflame-retardant properties, as discussed in further detail below. Theouter layer 64 may also have a continuous annular cross-section.

FIG. 3 is a partial cross-sectional view of the armored fiber opticassembly 20 of FIG. 2 taken along the line 3-3. In FIG. 3, the opticalfibers 94 and the strength members 98 are omitted so that certaindimensions of the assembly 20 can be illustrated. For the purposes ofsimplicity in illustration, the dielectric armor 50 is depicted with auniform circular cross-section that does not reflect the spiral of thearmor profile.

As shown in FIG. 3, the fiber optic assembly 80 has an outer radiusR_(C) and the dielectric armor 50 has an inner radius R_(I). Theassembly 20 can include a free space 100 disposed between the outersurface of the fiber optic assembly 80 and the inner surface of thedielectric armor 50 generally represented by a separation ΔR. While theseparation ΔR between the cable jacket 90 and the armor 50 inner surfaceis shown as uniform around the jacket circumference, it will in factvary along the length of the fiber optic assembly 20, and the cablejacket 90 and the armor 50 will actually contact one another at numerouspoints. An average or median separation ΔR can therefore be calculatedas ΔR=R_(I)−R_(C). The presence of the free space 100 improves opticalperformance during crush events and the like as discussed below. By wayof example, the average free space separation ΔR is typically about 2millimeters or less, but free space separation ΔR values larger than 2millimeters are possible. In one embodiment, the free space separationΔR is between 0.1-1.5 millimeters. In a second embodiment, the freespace separation ΔR is in the range of 0.4-0.6 millimeters.

Mechanical characteristics used in designing the armored fiber opticassembly 20 include minimum bend radius, impact resistance,crush-resistance, tensile strength, durability of the dielectric armor,susceptibility to plastic deformation, the ability to recover from crushloads, etc. Material characteristics such as the hardness, modulus,etc., along with geometry influence the desired characteristics/opticalperformance for the armored fiber optic assembly 20. For instance, theinner layer 62 and/or the outer layer 64 of the armor 50 should have asuitable modulus of elasticity. By way of example, a modulus ofelasticity at 1% strain for the rigid material (the inner layer 62 inthe illustrated embodiment) is about 1200 MPa or greater and the modulusof elasticity at 1% strain for the non-rigid material (the outer layer64 in the illustrated embodiment) is in the range of 300-1200 MPa. Theseare merely explanatory examples and other values for the modulus ofelasticity are possible with the concepts disclosed herein.

EXAMPLE 1

A fiber optic assembly as illustrated in FIG. 2 has an overall averageoutside diameter of about 10.4 mm, allowing for some ovality in thecross-section, an average outer layer 64 thickness of about 1.0 mm, anaverage inner layer 62 thickness in the range of about 1.1-1.2 mm, acable jacket 90 thickness of about 0.5 mm, an assembly 80 outsidediameter of about 5.6 mm, and a median separation ΔR in the range ofabout 0.3-0.6 mm. The cable jacket 90 and the outer layer 64 are madefrom AlphaGary SG III 1070L, and the inner layer 62 is made from TeknorApex flame retarded rigid PVC available under the designation FG RE8015B. The fiber optic assembly 80 included 12 optical fibers of flameretarded tight-buffered fibers. The armored fiber optic assembly 20 hada weight of about 99.1 kilogram per kilometer, with the fiber opticassembly 80 accounting for about 32.2 kilogram per kilometer, and theinner layer 62 of the armor 50 accounting for about 36.1 kilogram perkilometer.

EXAMPLE 2

A fiber optic assembly as illustrated in FIG. 2 has an overall averageoutside diameter of about 11.3 mm, allowing for some ovality of thecross-section, an average outer layer 64 thickness of 1.0 mm, an averageinner layer 62 thickness in the range of about 1.1-1.2 mm, a cablejacket 90 thickness of about 0.5 mm, an assembly 80 outside diameter ofabout 6.8 mm, and a median separation ΔR in the range of about 0.3-0.6mm The cable jacket 90 and the outer layer 64 are made from AlphaGary SGIII 1070L, and the inner layer 62 is made from Teknor Apex flameretarded rigid PVC available under the designation FG RE 8015B. Thefiber optic assembly 80 included 24 optical fibers of flame retardedtight-buffered fibers. The armored fiber optic assembly 20 had a weightof about 145.1 kilogram per kilometer, with the fiber optic assembly 80accounting for about 56.0 kilogram per kilometer, and the inner layer 62of the armor 50 accounting for about 52.1 kilogram per kilometer.

EXAMPLE 3

A plenum rated fiber optic assembly as illustrated in FIG. 2 has anoverall average outside diameter of about 10.6 mm, allowing for someovality in the cross-section, an average outer layer 64 thickness ofabout 1.2 mm, an average inner layer 62 thickness in the range of about1.1-1.2 mm, a cable jacket 90 thickness of about 0.5 mm, an assembly 80outside diameter of about 5.2 mm, and a median separation ΔR in therange of about 0.3-0.6 mm The cable jacket 90 and the outer layer 64 aremade from AlphaGary SG III 1070L, and the inner layer 62 is made fromTeknor Apex flame retarded rigid PVC available under the designation FGRE 8015D. The fiber optic assembly 80 includes 12 optical fibers offlame retarded tight-buffered fibers. The armored fiber optic assembly20 has a weight of about 138.7 kilogram per kilometer, with the fiberoptic assembly 80 accounting for about 27.4 kilogram per kilometer, andthe inner layer 62 of the armor 50 accounting for about 35.6 kilogramper kilometer.

EXAMPLE 4

A plenum rated fiber optic assembly as illustrated in FIG. 2 has anoverall average outside diameter of about 13.2 mm, allowing for someovality of the cross-section, an average outer layer 64 thickness of 1.5mm, an average inner layer 62 thickness in the range of about 1.3-1.4mm, a cable jacket 90 thickness of about 0.5 mm, an assembly 80 outsidediameter of about 6.65 mm, and a median separation ΔR in the range ofabout 0.3-0.6 mm. The cable jacket 90 and the outer layer 64 are madefrom AlphaGary SG III 1070L, and the inner layer 62 is made from TeknorApex flame retarded rigid PVC available under the designation FG RE8015D. The fiber optic assembly 80 includes 24 optical fibers of flameretarded tight-buffered fibers. The armored fiber optic assembly 20 hasa weight of about 189.2 kilogram per kilometer, with the fiber opticassembly 80 accounting for about 45.5 kilogram per kilometer, and theinner layer 62 of the armor 50 accounting for about 52.7 kilogram perkilometer.

One mechanical property provided by the dielectric armor 50 is itsresistance to crush under loads. FIG. 4 illustrates the fiber opticassembly 20 under crush load testing in a test apparatus 200. The testapparatus 200 includes two rigid plates 202, 204 of 10 centimeter lengthLP in FIG. 4. The plates 202, 204 are configured to exert compressiveloads at a mid-span section of a cable. Edges of the plates 202, 204 canbe rounded so that the plates do not cut into the surface of theassembly 20. The test apparatus 200 can be used to test, for example,the ability of the fiber optic assembly 20 to recover its original shapeafter being subjected to crush loads. While the load required to deflectthe dielectric armor 50 generally is lower than metallic BX-type armors,the deformation is not as severe, and most or all of the attenuation inoptical signals conveyed by the assembly 20 is relieved after removingthe test load. By contrast, metallic armors deform plastically, so thatthey may recover little, if at all, after removing a test load. Theelastic properties of the rigid dielectric material for inner layer 62allow the armor 50 to recover generally to its original shape aftercrush or impact.

For rigid PVC materials, such as Teknor Apex materials FG RE 8015A,8015B and 8015D, the elastic region along the stress/strain curvedefines where the dielectric armor will return to its original shape.The elastic deformation region of the dielectric armor 50 is defined ona stress/strain curve generated from a flexural modulus test. If theelastic region is exceeded, the dielectric armor 50 yields (orplastically deforms) 180 degrees apart and may recover to an oval shape.According to one aspect of the present embodiments, the dielectric armorcable 50 has superior resistance to crush loads. According to a furtheraspect, even if a crush rating, such as ICEA S-83-596-2001, is exceeded,the fiber optic assembly 20 significantly or substantially whollyrecovers its original shape after removal of the crush load. ICEAS-83-596-2001 covers fiber optic communications cables intended for usein buildings. Cables according to the present embodiments can also bedesigned to recover after testing under ICEA S-104-696, which coversfiber optic communications cables intended for indoor and outdoor use,and testing under ICEA S-87-640, which covers fiber optic communicationscables intended for outdoor use.

Crush testing may cause unacceptable optical attenuation in the opticalfibers 94. According to another aspect of the present embodiments, underthe described test conditions, assuming none of the optical fibers 94are damaged, attenuation caused by the crush load is relieved when thecrush load is removed. By contrast, if a BX cable crush/impact rating isexceeded and the armor plastically deforms, the cable typically remainspinched resulting in a permanent attenuation step in the cable.

Fiber optic assemblies as described in Example 1 (12 fiber), and Example2 (24 fiber) were subjected to crush testing under extremely high loadsin an apparatus as generally depicted in FIG. 4. Table A listed belowsummarizes the results for crush testing for the exemplary assemblydescribed in Example 1 (12 fiber count cable). Table B listed belowsummarizes the results for crush testing for the assembly described inExample 2 (24 fiber count cable). The test procedure and results arediscussed below.

Referring to FIG. 4 and to Tables A and B, the crush test loads(Newtons), were applied over an axial length LP of 10 centimeters.Several different Locations along the length of the two assemblies werecrush tested. The opposed plates 202, 204 applied crush loads in the “z”or “crush” direction, which was aligned with an initial, pre-crushoutside diameter at each location of the assembly. In Tables A and B,average, pre-crush outside diameters of the assemblies are used forcomparison purposes because the assemblies may have some degree ofovality in cross-section. The test began by advancing the plates 202,204 together in the z-direction to apply an initial crush load to theassemblies. The initial load compressed the assembly in Table A to aninitial crush height of about 10.11 mm, and the assembly of Table B toan initial crush height of 10.8 mm. The height of the compressedassembly is assumed to be the spacing of the plates 202, 204 duringcrush testing. The initial crush load is applied to generally alignpeaks on the assembly profile between the plates 202, 204.

The crush load was then increased to the Maximum Force (Newtons). TheMaximum Force corresponded to the maximum force that could be generatedby the test apparatus 200, which fell in the range of about 8,000 N. Atthis time, the armored cable assembly was pressed between the plates202, 204 at the Plate Spacing at Maximum Crush (mm) The armored assemblywas held at that load for 10 minutes. The Percent of Outside Diameter atCrush percentages reflect the Plate Spacing at Maximum Crush valuesdivided by the pre-crush Outside Diameter of the assembly. Thiscalculation indicates the degree to which the assembly was crushed fromits pre-crush state. The test crush load was then released and theassembly was allowed to recover for five minutes. The Cable DimensionAfter Recovery, now reduced in height from the original OutsideDiameter, was then measured in the crush or z-direction. The Percent ofOutside Diameter After Recovery percentages reflect the Cable DimensionAfter Recovery values divided by the pre-crush Outside Diameter of theassembly.

TABLE A Crush Performance Testing - 12 Fiber Assembly with 10.4 mmPre-Crush Outside Diameter % of Cable Dim. % of Plate Spacing MaximumOutside After Outside Loca- at Maximum Force Dia. at Recovery Dia. Aftertion Crush (mm) (Newton) Crush (mm) Recovery 1 6.38 8024 61.3% 7.7874.8% 2 5.75 8011 55.3% 7.94 76.3% 3 5.52 8064 53.1% 7.33 70.5%

TABLE B Crush Performance Testing - 24 Fiber Assembly with 11.3 mmPre-Crush Outside Diameter % of Cable Dim. % of Plate Spacing MaximumOutside After Outside Loca- at Maximum Force Dia. at Recovery Dia. Aftertion Crush (mm) (Newton) Crush (mm) Recovery 1 6.51 8020 57.6% 9.3983.1% 2 6.37 8227 56.4% 8.01 70.1% 3 6.28 8033 55.6% 8.24 72.9%

The test data indicate that even after severe compression the testedassemblies recovered substantially along the crush dimension. Forexample, each of the 12 fiber assemblies in Table A experienced areduction to less than 62% of the original Outside Diameter duringMaximum Crush, yet recovered to have a dimension along the crushdirection that was at least 70% of the Outside Diameter. Each of the 24fiber assemblies in Table B experienced a reduction to less than 58% ofthe Outside Diameter during Maximum Crush, yet recovered to have adimension along the crush direction that was at least 70% of the OutsideDiameter. The 8000 Newton or greater loads applied to the testedassemblies were also extremely high when compared to conventional crushtest standards. For example, under ICEA S-83-596-2001, a 100 Newton percentimeter of cable test load is applied. For a 10 centimeter section,as applied in present case, the total load would amount to only 1000Newtons.

After crush testing, the assemblies were tested for optical attenuationand all had a delta attenuation of less than 0.4 decibels at 1550 nm.

Those skilled in the art will appreciate the difficulty in satisfyingthe required mechanical, low-smoke, and/or flame-retardantcharacteristics etc. for armored fiber optic assemblies.

The NFPA 262 plenum burn rating is especially stringent. The largecombustible polymer mass of the armored fiber optic assemblies rendersit difficult to meet both mechanical and flame/smoke requirements.Advantageously, certain embodiments of the armored fiber opticassemblies meet both the mechanical and the flame/smoke requirementssuch as riser-ratings and/or plenum-ratings. The cable described inExample 5 is expected to satisfy the ICEA S-83-596-2001 crush standard,and satisfies NFPA 262.

EXAMPLE 5

A fiber optic assembly as generally illustrated in FIG. 2 has an averageoverall outside diameter of 13.1 mm, allowing for some ovality ofcross-section, an outer layer 64 thickness of about 1.5 mm, an averageinner layer 62 thickness of about 1.3 mm, a cable jacket 90 thickness ofabout 1.0 mm, an assembly 80 outside diameter of about 7.8 mm, and amedian separation ΔR in the range of about 0.3-0.6 mm. The cable jacket90 and the outer layer 64 are made from AlphaGary SG III 1070L, and theinner layer 62 is made from Teknor Apex flame retarded rigid PVCavailable under the designation Teknor Apex material FG RE 8015D. Thefiber optic assembly 80 includes 24 tight-buffered optical fibers.

Mechanical and burn characteristics for the inner armor layer 62 arelisted below in Table C. The inner layer 62 in Example 5 conforms withthese properties.

TABLE C Preferred Properties for Inner Armor Layer MaterialCharacteristic Min Max Tensile (psi) 6,000 — Tensile Modulus (psi)300,000 — Elongation (%) 100% — Flexural Modulus (psi) 300,000 — LOI 46— Cone Calorimeter @ 75 kW/m2 (⅛″ thick specimen) Peak Smoke (1/m) — 1.5Peak Heat Release (kW/m²) — 110 Average Heat Release (kW/m²) — 78Average Heat of Combustion (MJ/kg) — 9 Total Heat Released — 65

Preferred mechanical and burn characteristics for the outer jacket layer64 and the cable jacket layer 90 are listed below in Table D. The layers64, 90 in Example 5 conform with these properties.

TABLE D Preferred Properties for Jackets Core Jacket & Outer jacketMaterial Characteristic Min Max Tensile (psi) 2400 — Elongation (%) 160%—

The PVC/PVC combination of Example 5 results not only in the desiredflame-retardant riser rating, but also has the desired mechanicalrobustness for the rating.

The embodiments discussed above describe specific materials for assemblycomponents to meet desired mechanical and burn characteristics. Ingeneral, if intended for indoor use, the armored fiber optic assembly 20is flame-retardant and has a desired flame-retardant rating depending onthe intended space, such as plenum-rated, riser-rated, general-purpose,low-smoke zero-halogen (LSZH), or the like. Suitable materials for thelayers 62, 64 of the dielectric armor 50 may be selected from one ormore of the following materials to meet the desired rating: polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), flame-retardantpolyethylene (FRPE), chlorinated polyvinyl chloride (CPVC),polytetraflourethylene (PTFE), polyether-ether keytone (PEEK),Fiber-Reinforced Polymer (FRP), low-smoke zero-halogen (LSZH),polybutylene terephthalate (PBT), polycarbonate (PC), polyethylene (PE),polypropylene (PP), polyethylene terephthalate (PETE), andacrylonitrile-butadiene-styrene (ABS).

Another example of an armored fiber optic assembly similar to FIG. 2 andhaving a riser rating includes an inner layer 64 formed from a PVCavailable from Teknor Apex under the tradenames FG RE 8015A, 8015B and8015D, and an outer layer 62 is formed from a plenum-grade PVC jacketmaterial available from AlphaGary under the designation SG III 1070L.This PVC/PVC combination also meets the desired mechanical robustnessfor the rating ICEA S-83-596-2001.

An added advantage in the use of dielectric armor is the relatively lowweight of the armor layer 62. As shown by Example 1, the 12 fiberdielectric armor assembly 20 has a weight of about 99.1 kg/km, and asshown in Example 3, a weight of 138.7 kg. As shown by Example 2, the 24fiber dielectric armor assembly 20 has a weight of about 145.1 kg/km,and as shown by Example 4, a weight of 189 kg. In the presentembodiments, the weight of the inner layer 62 of armor surrounding thefiber optic assembly can be less than 40% of the total weight of thearmored cable assembly, and can even be as low as less than 30% of thetotal weight of the assembly.

FIG. 5 is an enlarged partial cut-away perspective view and FIG. 6 is aclose-up view of the armored fiber optic assembly 20 of FIG. 2. FIG. 6illustrates a partial longitudinal cross-section of the dielectric armor50 superimposed on a grid G for referencing the shapes of the layers.The armored profile 54 has a pitch P that includes a web 102 and a band110. The pitch P describes a generally repeating shape that forms thearmored profile in a spiral manner along the longitudinal axis of theassembly 20. The geometry of the armored profile 54 is discussed belowin more detail with respect to finite-element modeling performed. Asbest shown in FIG. 6, the armored profile 54 of this embodiment isgenerally formed with inner layer 62 having a curvilinear profile formedin a spiral along the longitudinal axis and outer layer 64 has agenerally uniform thickness formed over the curvilinear profile of innerlayer 62. Two factors that influence the mechanical performance of thedielectric armor are geometry of the armored profile and the materialcharacteristics of the layers.

FIG. 7 depicts an enlarged cross-sectional view of a portion of thedielectric armor 50 of FIG. 2 superimposed on grid G with certaindimensions of the armor profile shown. The dielectric armor isillustrated with a web 102 and a band 110. The inner layer 62 of theband 110 has a thickness T1 and the web 102 of the inner layer 62 has athickness T2. On grid G, a web thickness T2 is defined asT2=T1−d_(O)−d_(i), where an outer groove depth d_(O) is the heightdifference between the band 110 and the web 102 of the inner layer 62,and an inner groove depth d_(i) is the height difference between theband 110 and the web 102 of the inner layer 62. A total groove depthd_(O)+d_(i) is the sum of the outer groove depth d_(O) and inner groovedepth d_(i). In this illustration, the outer layer 64 has a thickness T3that is essentially uniform along the length of the armor profile, buteither or both of the layers could have the undulating armor profile.The dielectric armor 50 has an inner radius R_(I) and an outer radiusthat is equal to R_(I)+T₁.

FIG. 8 is an enlarged perspective view of a portion of the layer of thedielectric armor 50 having the armor profile showing genericgeometry/dimensions used for finite-element modeling of the armor. FIG.8 depicts an armor profile that is shaped very closely to a stepprofile, which provides excellent mechanical characteristics when theproper geometry is selected. However, in practice it is difficult tomanufacture the armor profile nearly as a step profile at relativelyhigh line speeds as shown in FIG. 8. Consequently, manufactureddielectric armor has a rounded or sloped profile as shown in FIG. 7.

Finite-element analysis was conducted on the model of FIG. 8 to simulatethe shape of manufactured profiles like shown in FIG. 7. Usingfinite-element analysis, the inventors discovered certain dimensionsand/or relationships that provide desired mechanical characteristics forthe armored profile. FIG. 8 depicts one-half pitch P/2 for the armoredprofile (i.e., the one-half pitch P/2 only depicts a fraction of the web102 and a fraction of the band 110. The one-half pitch P/2 of the armorprofile has a length given by the sum of length L1 (i.e., the fractionalportion of the band), length L_(T) (i.e., a transitional portion betweenthe band and web), and length L2 (i.e., the fractional portion of theweb). Additionally, for the purpose of simplicity only the layer withthe armor profile of the dielectric armor was modeled since itcontributes to the majority of the mechanical characteristics for thedielectric armor. Consequently, the web 102 has a length referred to asa groove length 2(L2) herein, which is two times the length L2.

The dielectric armor 50 can be formed by extrusion. FIG. 9 depicts aschematic side view of an extrusion system 300 that includes an extruder302 having an interior 301, with a barrel 303 and a screw 310 in theinterior 301 and attached to a crosshead assembly (“crosshead”) 304.X-Y-Z Cartesian coordinates are included for spatial reference, withFIG. 9 illustrated in the X-Y plane. The extruder 302 includes a screw310 that is mechanically connected to and driven by a motor assembly320. The motor assembly 320 includes a motor 322 and a drive system 324that connects the motor to the screw 310. A material hopper 330 providesextrusion material 332—here, the dielectric material that ultimatelymakes up dielectric armor 50—to the extruder 302. U.S. Pat. No.4,181,647 discloses an exemplary extrusion system that is suitable foradaptation for use as the extrusion system 300.

FIG. 10 is a close-up, partial cross-sectional schematic view of anexplanatory crosshead 304 as viewed in the Y-Z plane. The crosshead 304includes a tip 348 having a central channel 350 with an output end 352and in which is arranged a profile tube 360 having an outer surface 361,an inner surface 362 that defines a tube interior 363, a proximal(output) end 364, and a distal end 365. A profiling feature 370 islocated on outer surface 361 at output end 352. In an exampleembodiment, the profiling feature 370 is a protrusion such as a nub or abump. The profile tube interior 363 is sized to accommodate the fiberoptic assembly 80 as it advances axially through the interior 363. Theprofile tube distal end 365 is centrally engaged by a gear 374 that, inturn, is driven by a motor (not shown) in a manner such that the profiletube 360 rotates within channel 350.

The crosshead 304 further includes a die 378 arranged relative to thetip 348 to form a cone-like material channel 380 that generallysurrounds the central channel 350 and that has an output end 382 in thesame plane as channel output end 352. The material channel 380 isconnected to the extruder interior 301 so as to receive extrusionmaterial 332 therefrom and through which flows the extrusion materialduring the extrusion process to form one or more layers of thedielectric armor. In the example embodiment of the crosshead 304 of FIG.10, a profile tube output end 365 extends beyond the channel output end352 such that the profiling feature 370 thereon resides adjacentmaterial channel output end 382. In an example embodiment, the profiletube 360 and the tip 348 are integrated to form a unitary, one-piecetool.

In forming armored fiber optic assemblies 20, extrusion material (notshown) flows through the material channel 380 and out of the materialchannel output end 382. At the same time, the fiber optic assembly 80 isfed through the profile tube interior 363 and out of profile tube outputend 364 (and thus through the tip 348 and the die 378). In the meantime,the profile tube 360 is rotated via the gear 374 so that profilingfeature 370 redirects (i.e., shapes) the flow of the extrusion materialas it flows about fiber the optic assembly 80. As the fiber opticassembly 80 moves through the profile tube output end 364, the circularmotion of the profiling feature 370 diverts the flow of extrusionmaterial. The combined motion of the profiling feature 370 and thelinear motion of fiber optic assembly 80 forms the armored profile. Thespeed at which profile tube 360 rotates relative to the motion of fiberoptic assembly 80 (which may also be rotating) dictates the pitch of thearmor profile. All other factors being equal, a higher rotational speedfor the profiling feature 370 results in a shorter pitch for the armorprofile. The size and shape characteristics of the profiling feature 370dictate, at least in part, the particular armor profile imparted to theouter surface 52 of the dielectric armor 50. Though the extrusion flowis primarily diverted on the interior of the armor, the drawdown of thematerial moves the groove partially or completely to the outer surfaceof the armor. Of course, this type of extrusion set-up may be used onany desired layer of the dielectric armor.

Additionally, there are other suitable methods for forming the armorprofile. By way of example, FIG. 11 schematically illustrates thedielectric armor 50 initially being extruded as a smooth-surfaced tube(i.e., having a smooth outer surface as shown on the right side).Thereafter, the armor profile of the outer surface 52 is then formed inthe smooth-surfaced tube, prior to hardening, by the application (e.g.,pressing) of a deforming member 402 (e.g., a nub or a finger) into thelayer so as to shape outer surface 52 in a manner similar to that usedin a lathe. In this example, the deforming member 402 may simply divertmaterial from the web to the band, or it may remove material entirelyfrom the dielectric armor 50. In one example embodiment, the deformingmember 402 is stationary and the assembly 20 is rotated, while inanother example embodiment, the deforming member 402 rotates around thedielectric armor 50 as it advances axially. In still another exampleembodiment, both the dielectric armor 50 and the deforming member 402rotate. The deforming member 402 may also be integrated into theextrusion tooling (die).

FIG. 12 is a close-up, schematic cross-sectional view of anotherexplanatory embodiment of crosshead 304′ similar to that shown in FIG.10. In FIG. 12, the tip 348 and the die 378 are configured so thatcentral channel 350 is combined with the material channel through whichthe extrusion material flows. A portion of the profile tube 360 residesin an interior region 349 of the tip 348, while the proximal end portionof the profile tube resides within the channel 350 so that the profilingfeature 370 resides within central channel 350 adjacent to the channeloutput end 352. This geometry confines the extrusion material 332 withinthe die 378 while allowing for control of the flow of extrusionmaterial.

In another explanatory embodiment similar to that shown in FIG. 11 andas illustrated in FIGS. 13 and 14, the dielectric armor is initiallyextruded as a smooth-surfaced tube (i.e., having a smooth outer surfaceon the right side) of dielectric extrusion material 332. The armorprofile of the outer surface 52 is then formed prior to hardening, bythe application (e.g., pressing) of a deforming member 402 (e.g., a setof gears) having one or more features 404 that press into the dielectricarmor in order to shape the outer surface 52. FIG. 14 shows aperspective view of an exemplary embodiment of a roller-type deformingmember 402 having an outer edge 403 in which features 404 are formed. Inthis embodiment, the deforming member 402 of FIG. 13 may be formed insets of two, three, four, or more for forming the desired armor profile.The roller-type deforming member 404 rolls over the outer surface 52 ofthe dielectric armor before it hardens to impress features 404 of thearmor profile.

The deforming member 402 may press extrusion material 332 against thefiber optic assembly 30 to eliminate free space 100. The deformingmember 402 may also press against the dielectric armor 50 in a mannerthat maintains the desired amount of free space 100. FIG. 15 is a frontview that illustrates the use of two roller-type deforming member toimpress the desired armor profile into the dielectric armor.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention.

We claim:
 1. An armored fiber optic assembly, comprising: a fiber opticassembly having at least one optical fiber; and armor comprising apolymer surrounding the fiber optic assembly, the armor having an armorprofile with an outside diameter, wherein when a 10 cm section of thefiber optic assembly is subjected to a crush load along a crushdirection between opposing plates that reduces a crush dimension of theassembly from the outside diameter to about 60 percent of the outsidediameter, the cable assembly recovers when the crush load is released sothat the crush dimension increases to at least 70 percent of the outsidediameter.
 2. The armored fiber optic assembly of claim 1, wherein the atleast one optical fiber comprises at least twelve optical fibers.
 3. Thearmored fiber optic assembly of claim 1, wherein when the armor issubjected to a crush load along a crush direction that reduces the crushdimension of the assembly from the outside diameter to about 60 percentof the outside diameter, the cable assembly recovers so that the crushdimension increases to at least 74 percent of the outside diameter. 4.The armored fiber optic assembly of claim 1, wherein the armored fiberoptic assembly has a median separation in the range of about 0.1-1.5millimeters between the fiber optic assembly and an interior of thearmor.
 5. The armored fiber optic assembly of claim 1, wherein the armorcomprises an inner layer and an outer layer.
 6. The armored fiber opticassembly of claim 5, wherein the inner layer has a continuous annularcross-section.
 7. The armored fiber optic assembly of claim 5, whereinthe inner layer comprises a PVC.
 8. The armored fiber optic assembly ofclaim 5, wherein the armored fiber optic assembly satisfies ICEAS-83-596-2001.
 9. The armored fiber optic assembly of claim 5, whereinafter the crush load is released, the at least one optical fiber has adelta attenuation due to the crush load of less than 0.4 decibels at1550 nanometers.
 10. The armored fiber optic assembly of claim 5,wherein the inner layer has a modulus of elasticity of about 1200 MPa orgreater.
 11. The armored fiber optic assembly of claim 5, wherein thearmor has an outside diameter in the range of 8-15 millimeters.
 12. Thearmored fiber optic assembly of claim 11, wherein the inner layer is aPVC and the outer layer is a PVC.
 13. The armored fiber optic assemblyof claim 1, wherein the armor profile has a pitch P between 5millimeters and 30 millimeters and a groove length that is between 20percent and 80 percent of the pitch P.
 14. The armored fiber opticassembly of claim 13, wherein the armor comprises an inner layer with aShore D hardness and an outer layer with a Shore D hardness that islower than that of the inner layer.
 15. An armored fiber optic assembly,comprising: a fiber optic assembly having at least one optical fiber, anextruded polymer cable jacket, wherein the fiber optic assembly is astranded tube cable; and armor comprising a polymer surrounding thefiber optic assembly, the armor having an outer surface with anundulating geometry along its length, wherein when a 10 cm section ofthe fiber optic assembly is subjected to a crush load along a crushdirection between opposing plates that reduces a crush dimension of theassembly from the outside diameter to about 60 percent of the outsidediameter, the cable assembly recovers when the crush load is released sothat the crush dimension increases to at least 70 percent of the outsidediameter.
 16. The armored fiber optic assembly of claim 15, whereinafter the crush load is released, the at least one optical fiber has adelta attenuation due to the crush load of less than 0.4 decibels at1550 nanometers.
 17. The armored fiber optic assembly of claim 15,wherein the armor has a layer having a modulus of elasticity of about1200 MPa or greater.
 18. The armored fiber optic assembly of claim 15,wherein the armor has an outside diameter in the range of 8-15millimeters.
 19. An armored fiber optic assembly, comprising: a fiberoptic assembly having at least one optical fiber, an extruded polymercable jacket, wherein the fiber optic assembly is a stranded tube cable;and a dielectric armor surrounding the fiber optic assembly, thedielectric armor having an outer surface with an undulating geometryalong its length, wherein when a 10 cm section of the fiber opticassembly is subjected to a crush load along a crush direction betweenopposing plates that reduces a crush dimension of the assembly from theoutside diameter to about 60 percent of the outside diameter, the cableassembly recovers when the crush load is released so that the crushdimension increases to at least 70 percent of the outside diameter. 20.The armored fiber optic assembly of claim 19, wherein the armored fiberoptic assembly has a median separation in the range of about 0.1-1.5millimeters between the fiber optic assembly and an interior of thedielectric armor.